According to a number of narrations, when Muslim b. 'Aqil arrived in Kufa at first he went to Muslim b. 'Awsaja's house. People gathered there to take oath of allegiance. They swore to Allah they would defend Imam al-Husayn (a) to their last breath. They sent letters to Imam al-Husayn (a) about the allegiance of people. Then Imam al-Husayn (a) began his travel to Kufa. Muslim b. 'Awsaja played a crucial role in all these events.

The spy of 'Ubayd Allah b. Ziyad, Ma'qil, found the safe house of Muslim b. 'Aqil through Muslim b. 'Awsaja.

After Hani b. 'Urwa was arrested, Muslim b. 'Aqil chose commanders for his army in order to organize the soldiers; he assigned Muslim b. 'Awsaja as the commander of Banu Asad and Madhhij.

Following the arrest and martyrdom of Hani b. 'Urwa and Muslim b. 'Aqil, Muslim b. 'Awsaja decided to hide in a safe house. Then after the arrival of Imam al-Husayn (a), he joined Imam's army with his family in Karbala.

In Karbala

According to some narrations Muslim b. 'Awsaja's wife and children attended the Battle of Karbala. As historians said: "Khalaf b. Muslim b. 'Awsaja, his brave son, were fighting alongside his father in the Battle of Karbala until finally he was martyred in the battle. According to some reports: a young boy came out of the tents while his mother was after him; the boy was Muslim b. 'Awsaja's son.

The Night before 'Ashura'

At the night before 'Ashura', when Imam al-Husayn (a) told his soldiers: you are allowed to leave Karbala and your promises and oath of allegiance have served well so far, you are not obligated to stay for the battle. Then, some companions declared their loyalty to Imam al-Husayn (a) over again. After the descendants of Banu Hashim, Muslim b. 'Awsaja was the first one who said:

Oh, Abu 'Abd Allah! We would never leave you alone. How is it possible to bring excuses to Allah? O, by Allah, never! We will never leave you alone; I will never give up; I will slay the enemies with my spear and sword until it drops on the ground; then I stone them. By Allah, I would never leave you alone until I fulfill my duties to Allah and defend the descendants of Prophet Muhammad (s). O, by Allah, if I am perished, I would reborn, and then if I am burnt and turned into ashes, I would reborn; and if it happens seventy times I would reborn and fight for you until I am martyred for you. I would never leave you as I know I will be perished once. Consequently, eternal prosperity and dignity would be mine.

Imam al-Husayn (a) expressed gratitude to each one of them and returned his tent.

The Day of 'Ashura'

As Al-Shaykh al-Mufid said: Imam al-Husayn (a) and his soldiers dug a trench around the rear part of their tent and set fire inside it. After seeing the flaming fire, Shimr b. Dhi l-Jawshan shouted: O Husayn! You are preparing fire of this world for yourself before the judgment day?! Imam al-Husayn (a) replied: Who is that man? Is he Shimr b. Dhi l-Jawshan? Then Imam (a) referred to Sura Maryam, verse 70 and said: O goatherd boy! You deserve flames of Hell! Then Muslim b. 'Awsaja was ready to kill Shimr with an arrow and asked for Imam Hysayn's permission; however Imam rejected his request and said: I do not want to commence the battle.

His Motto in the Battle

The mystical and knowledgeable mottos of Muslim b. 'Awsaja should be highly regarded, which represent his deep understanding of the principles of Ahl al-Bayt (a). He repeatedly uttered this motto in the battles:

If you desire to know me, I am brave as a lion; my lineage goes back to Banu Asad. If you treat me with tyranny, you are strayed from the right path, and you are guilty of ingratitude toward Allah.

Martyrdom

After fighting the enemy soldiers in the Battle of Karbala, Muslim b. 'Awsaja had numerous injuries and he was bleeding heavily, then he fell on the ground. Imam al-Husayn (a) and Habib b. Muzahir came by his side. Imam said: May God have mercy on your soul. Then he recited the verse:

Faminhum man qaza nahbahu wa minhum man yantaziru wa ma baddalu tabdila (Of them (believers) some have completed their vow to (the extreme) and some still wait, but they have never changed (their determination) in the past.) Al-Ahzab, verse 23.

Then Habib b. Muzahir said to him: "your loss is hardly tolerable to me, but I give glad tidings to you on Paradise". Muslim b. 'Awsaja replied with difficulties: May God send his blessing on you. Habib replied: I wish I could carry out what you desire as your will. Muslim replied: "I advise you to defend him (Imam al-Husayn (a)) to your last breath and never give up trying". And Habib replied: I accomplish what you desire and I will make you delighted.

According to Ziyarat al-Shuhada', Muslim b. 'Awsaja was the first one who was martyred in the Battle of Karbala. And Imam al-Husayn (a) promised him salvation by the name of Allah. While those who participated in the martyrdom of Muslim b. 'Awsaja are cursed by Imam al-Husayn (a).